Format C# files with spaces and POSIX compliance

[aaronfranke]

This PR is split into 3 commits:

• The first commit formats C# files for POSIX compliance, with a newline at EOF and correct line endings. This improves compatibility with tools that expect POSIX compliance, and GitHub shows a "No newline at end of file" warning if the newline at EOF is missing. Additionally, some tools will automatically fix these problems (I have my editors configured for this when possible), so this makes it easier to use those tools on this project without generating diffs. In this commit I also added a .gitattributes file so that Git should automatically fix line ending problems in the future.

• The second commit replaces tabs with 4 spaces. The C# indent style is to use 4 spaces, plus the .editorconfig already says to do this, but some files were using tabs, or had an inconsistent style. For example, I see this if I open src/Microsoft.Maui.Graphics/Color.cs on GitHub configured to show tabs as 8 characters wide:

• The third commit removes trailing space characters. Trailing space characters do nothing and should be deleted. Also, as with the first commit, when possible I have my editors configured to delete trailing whitespace, so this makes it easier to use those tools on this project without generating diffs.

I considered opening an issue first, but I figured it was easier to just open a pull request. There is already a .editorconfig that says to use spaces, so I know it's desired, yet many files in this repo aren't doing that.

I didn't format non-.cs files in this PR, since .cs files are the bulk of this repo, it makes sense to do the .cs ones separately from the rest. I can format other files in a future PR if desired.

[rmarinho]

we use tabs not spaces :)

[aaronfranke]

@rmarinho Then the .editorconfig should be updated, and the files that use spaces should be converted to tabs. I can do this if the project maintainers say it's desired.

[jonlipsky]

@aaronfranke If would be great if you'd like to contribute that change to the .editorconfig file.

[aaronfranke]

@jonlipsky Done.

[jonlipsky]

@aaronfranke I took another PR before yours, so now there are some conflicts. Care to resolve the conflicts so I can get your contribution in ASAP?

[aaronfranke]

@jonlipsky Done.

[jonlipsky]

Thanks so much for this!